Nylon 46 is a typical polyamide resin comprising tetramethylene diamine as a constituent, but for the melt polymerization method, which is a conventionally known nylon polymerization method in which an aqueous solution of the salt is concentrated under a pressure followed by relieving it to allow the temperature to rise above the melting point, it is difficult to produce nylon 46 with a high degree of polymerization because pyrrolidine resulting from intramolecular cyclization of tetramethylene diamine acts as a terminal blocking agent. Therefore, a special polymerization method is necessary to produce nylon 46 as described in Patent document 1.
Non-patent document 1 has described a method in which the oligomer obtained by heating a nylon 46 salt in a closed system is polymerized in solid or melt state. The melt polymerization method, however, has the problem of liability to an upper limit to the degree of polymerization and coloring of the product, and as described in Patent document 1, solid phase polymerization has been conventionally required to produce a white nylon 46 with a high degree of polymerization. Nylon 46 has another problem of being decomposed easily when melted, leading to a low melt retention stability.
There has been another nylon 46 production method which uses water and an organic solvent to perform interfacial polycondensation between tetramethylene diamine (water phase) and adipoyl chloride (organic phase). As described in Non-patent document 1, however, tetramethylene diamine is high in hydrophilicity and low in the rate of flow into the organic phase that contains adipoyl chloride, resulting a very low rate of polymerization. Furthermore, hydrolysis of adipoyl chloride takes place concertedly, making it very difficult to perform interfacial polycondensation up to a high degree of polymerization.
For production of nylons 48, 410, and 412, Patent document 2 has disclosed a two-step polymerization method that consists of oligomer preparation and solid phase polymerization as in the case of the nylon 46 production method.